Broadband communication technologies have made it practical to deliver full motion video and other programming services to individual users on demand. The term "broadband" describes a service or system having a transmission speed of 1.5 Mbps (megabits per second) or greater. It also refers to the characteristics of any network technology that multiplexes multiple, independent network carriers onto a single cable, usually using frequency division multiplexing. The broadband platforms that are currently available, either on a commercial scale or on an experimental basis, include upgraded cable systems using cable modems, upgraded telephone delivery systems using the Asymmetric Digital Subscriber Line (ADSL) technology, and satellite delivery systems that allow interactive communication.
A cable modem is a modem device that connects a personal computer (PC) to a coaxial or fiber optic cable that transmits television signals. Communication via a cable modem system is interactive. In an upgraded cable system, the bandwidth of the cable is typically divided into a relatively wide bandwidth for downstream data transmission (i.e. from the network to the PCs in the households) and a relatively narrow bandwidth for upstream signaling and telephony. A cable modem incorporates a tuner that separates data signals, broadcast streams and telephony signals. A cable modem may also include network management software by which the cable company can monitor the operation of the modem, as well as encryption devices.
Digital subscriber lines (DSL) technologies have been developed to provide broadband data communication over the existing copper wire twisted-pair telephone networks. Among the DSL technologies, asymmetric digital subscriber lines (ADSL) technology takes advantage of the asymmetrical nature of interactive multimedia communication. ADSL transmits downstream data through a high-speed channel to a subscriber's computer and upstream signals through a lower-speed channel to the network, while simultaneously providing "Plain Old Telephone Service" (POTS). This makes it possible to transmit full motion video over a standard telephone line.
Direct broadcast satellite (DBS) systems that are currently used for broadcast video transmission may also be used to provide broadband interactive data transmission. In a DBS system, data is typically transmitted from a geosynchronous communications satellite directly to a dish antenna attached to a personal computer. To return data, the subscriber may dial up a local service such as an Internet service provider (ISP) over a standard analog modem. A network of low orbit geosynchronous communications satellites has also been proposed to create a digital network around the globe.